Process for extracting alumina and potash from feldspar.



UNITED STACPE PATENT OFFICE.

SAMUEL PEACOCK, OF BALTIMORE, MARYLAND, ASSIGNOR '10 AMERICAN ACID COMPANY, OF BALTIMORE, MARYLAND, A CORPORATION OF MAINE.

PROCESS FOR EXTBAOTIN G ALUMINA AND POTASH FROM 'FELDSIAR.

No Drawing.

Specification of Letters Patent. Patented Aug, 13, 1912, Application filed April 8, 1911.

Serial No. 619,823.

To all whom z'tmay concern: Be it known that I, SAMUEL PEACOCK,

a citizen of'the United States, residing at Baltimore, in theState of Maryland, have invented certain new and useful Improve;

ments in Processes for Extracting Alumina and Potash from Feldspar; and I do hereby declare the following to be a full, clear, and

exact description of the invention, such as will enable others skilled in the art to WhlChf it appertains to make and use the same.

Th1s invention relates to a process for extracting alumina and potash from feldspar,

and has for its object to recover the potasnot be acted upon by the alkali present, unless the latter is in great excess.

With these ends in view, the inventionconsists in the novel steps constitutin particularly pointed out in the claims.

my? process more fully hereinafter disclose and; I

f is pulverized to not less than say 100 mesh As is well known, a typical feldsparcontains SiO A1 0 Fe,o,,,.K,'o, Na,O, CaO

and MgO; and there are a number of rocesses known or in use for the recovery 0 potash from feldspar, which involve the formation of calcium silicates and alkaline aluminates. One of the industrial defects in most of these processes, however, is, no account is taken of the fact that at the temperature of formation of calcium silicate by the dry process, a large proportion of the potash or soda present will be driven oflf by volatllization,

andtherefore the recovery of the alumina as such will be far below the quantity represented by the computed alumlnate, due to its compounds with lime. On the other hand, if a considerable excess of otash ori law of mass action, and the recovery of the alumina by forming a soluble aluminum 1 .salt is defeated.-

crush a mixture of feldspar -or similar I aluminiferous mineralr-to be decomposed,

chemical equivalents of calcium oxid .CaOv

and add sufiicient carbonate of lime to supply at least one and not "more than two to each chemical e uivalent of silica SiO sometimes to 1400, which is sufiicient to convert all the crystalline mineral material into the amorphous form. This latter operation is preferably conducted in a rotary kiln such as is ordinarily used in the manufacture of cement.

I have discovered in. calcining minerals containing potash and another metallic oxid which may develop basic properties such as lime, to a point suflicient to destroy the crystalline structure of the mineral, that all or substantially all of the potash present is dis laced or removed by volatilization. By

ad ing lime-stone, however, before the cal" cination takes place, there is produced a gas carryin potash which is comparatively high in car on dioxid CO, and which'may be utilized at a later stage in the process, as will appear below. By scrubbing such gas as it exits from the kiln any volatilized potash may be recovered as a carbonate.

After the mineral material is calcined, it

as is usually done in the manufacture of Portland cement, and it is then carefully sam led and its constituents determined. To t e pulverized mineral I next add sufiicient potash or soda to make, when computed with the otash or soda that has been found to alrea y exist in the calcined and pulverized material, one chemical e uivalent of pot-ash or soda to each' chemical equivalent of alumina present. The mixtureis next boiled, preferably under pressure, and with suflicient water to make a thin paste. The alumina then, becomes soluble as an alkali aluminate and the silica remains insoluble as a calcium silicate. The soluble and insoluble portions of the charge are next separated as by filtration, and the solu-* ble alkali aluminate is treated with carbon dioxid by means of whichnearly all the alkali is separated from the'alumina, probonate in substantial accordance with the 1 I, j following reaction 1 In carrying out my process, I firstcoarsely pound with alumina which resists, separation by filtration. This loss of alkali 1s.not

of commercial importance, butits presence in the alumina unfits the latter for certain process is'carefully sampled and its contents autoclave with superheated steam underof alkali and silica determined. Ithen add to the crude alumina sufiicient amorphous silica to form with such silica as is found present in the crude alumina, one equivalent of silica to each equivalent of soda or'pot ash found present in the said crude alumina. This mixture is next treated in a digester or pressure of substantially five atmospheres, more or less, as may be found necessary to decompose all the insoluble alkaline aluminates. The pressure and time of digestion is found dependent upon the amount of insoluble alkali aluminates present. The digester or autoclave charge is then filtered while hot and thoroughly washed with water, with the result that the silica and alkali are removed as an alkali silicate leaving a residuum of alumina. practically pure, and suitable for dehydration at high temperatures, which is adaptable for all the ordi-- nary industrial uses.

The carbon dioxid employed in the treatment of the alkali aluminate above, may be derived fromthat driven off from the kiln after it has gone through a scrubber, or of course it may be obtained from any other source. The volatilized alkali which escapes from the kiln with said gas is readily recovered in a scrubbing process as-a carbonate, and together with the carbonate derived from the alkali aluminate above, may be subjected to any suitable and well known process for the production of the oxid such as K 0, orit may be sold as a carbonate.

' The potassium oxi'd is conveniently formed by dissolving the carbonate in water and treating the solution with cal; cium oxid. Thusmixture of feldspar and carbonate of lime containing one and vnot more than two chemical equivalents of calcium oxid to cium 'oxid to each equivalent of silica contained in the feldspar; in calcining such mixture at a temperature sufficient to destroy the crystalline structure of the feldspar and to volatilize substantially all of the potash present while liberating carbon dioxid; and in suitably recovering the potash thus separated, substantially as described.

3. The process of recovering potash and alumina from feldspar, which consists in preparing a mixture of feldspar andcarbonate of lime containing one and not more than two chemical equivalents of calcium oxid to each chemical equivalent of silica contained. in the feldspar in order to later form an insoluble silicate of lime; in suitably heating such mixture and recovering the potash from the charge; then adding to said charge'sufiicient alkali to form one equivalentof potash for' each equivalent of alumina contained in said charge; boiling said charge with water to render the contained alumina soluble and the silica insoluble; separating the major portion of the potash from the soluble alumina; then adding amorphous silica tosaid aluminate in the proper proportion to produce a mixture containing one equivalent of silica to each equivalent of alkali remaining in said alumina; and finally suitably separating said alumina from said potash and silica, substantially as described.

In testimony whereof, I afix my signature, in. presence of two witnesses.

I SAMUEL PEACOCK. Witnesses T. W. WITHERSPOON,

R. M. PARKER. 

